Magnetic resonance tomography systems are imaging apparatuses, that in order to map an examination object, align the nuclear spins of the examination object with a strong external magnetic field and by a magnetic alternating field excite the nuclear spins for precession about this alignment. The precession or return of the spins from the excited state into a state with less energy in turn generates, as a response, a magnetic alternating field, also referred to as magnetic resonance signal, that is received by an antenna.
With the aid of magnetic gradient fields, a spatial encoding is impressed onto the signals, that permits an assignment of the received signal to a volume element. The received signal is evaluated and a three-dimensional imaging representation of the examination object is provided. The generated representation specifies a spatial density distribution of the spins.
Magnetic fields of 1.5 tesla, 3 tesla or higher as a BO field for alignment of the nuclear spins may be used in magnetic resonance tomography systems. Since the Larmor frequency increases linearly with the BO field strength, the Larmor frequency moves into ranges of 70 MHz to 150 MHz and above. Noise portions reduce with a higher frequency. However, the magnets required are at the same time becoming increasingly heavier and more expensive on account of growing inner forces. The energies stored in the fields are also increasing, so that ever more complicated safety measures are taken in the event of a failure of the superconductivity.
There is therefore an interest in reducing the necessary costs for the field magnets for cost-effective magnetic resonance tomography systems.
With lower BO field strengths and the correspondingly lower Larmor frequencies, the ratio of the size of the local coil to the wavelength is even more unfavorable. A resonance for the receiving process may only be achieved by a number of what are known as shortening capacitors, that require corresponding space and increase costs.